Skeletal System

Functions of the Skeletal System

The skeletal system provides the structural framework for the human body and serves several essential functions:

• Support: Provides support for the body and cradles soft organs.

• Protection: Protects vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Serves as levers for muscles to produce movement.

• Mineral Storage: Stores minerals, primarily calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Production: Houses red bone marrow, which produces blood cells (hematopoiesis).

• Triglyceride Storage: Stores fat in yellow bone marrow.

Classification of Bones by Shape

Bones are classified into four main groups based on their shapes:

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin, flattened, and usually curved (e.g., sternum, ribs, skull bones).

• Irregular Bones: Complicated shapes that do not fit other categories (e.g., vertebrae, hip bones).

Surface Bone Markings and Their Functions

Bone markings are structural features adapted for specific functions, such as muscle attachment or passage of nerves and blood vessels.

• Projections: Sites of muscle and ligament attachment (e.g., tuberosity, crest, trochanter).

• Surfaces: Form joints (e.g., head, facet, condyle).

• Depressions and Openings: Allow passage of blood vessels and nerves (e.g., foramen, fossa, groove).

Major Parts of Bone Tissue (Osteon)

The osteon (Haversian system) is the structural unit of compact bone.

• Central (Haversian) Canal: Contains blood vessels and nerves.

• Lamellae: Concentric rings of calcified matrix.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae, allowing for nutrient and waste exchange.

Parts of a Long Bone and Associated Bone Types

• Diaphysis: Shaft; composed mainly of compact bone.

• Epiphyses: Ends of the bone; mostly spongy bone covered by compact bone.

• Metaphysis: Region between diaphysis and epiphysis; contains the epiphyseal plate in growing bones.

• Medullary Cavity: Central cavity containing yellow marrow (fat storage).

• Periosteum: Outer fibrous covering.

• Endosteum: Thin membrane lining the medullary cavity.

Axial Skeleton

Overview and Components

The axial skeleton forms the central axis of the body and consists of:

• Skull: Cranial and facial bones.

• Vertebral Column: Cervical, thoracic, lumbar vertebrae, sacrum, and coccyx.

• Thoracic Cage: Ribs and sternum.

Bones and Landmarks of the Axial Skeleton

• Skull: Includes frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones; facial bones include maxilla, mandible, zygomatic, etc.

• Landmarks: Foramina (e.g., foramen magnum), processes (e.g., mastoid process), and sutures (e.g., coronal suture).

• Vertebral Column: 7 cervical, 12 thoracic, 5 lumbar vertebrae, sacrum, coccyx.

• Thoracic Cage: 12 pairs of ribs (true, false, floating), sternum (manubrium, body, xiphoid process).

Types of Vertebrae

• Cervical Vertebrae: Smallest, have transverse foramina; C1 (atlas) and C2 (axis) are specialized.

• Thoracic Vertebrae: Articulate with ribs; have long, downward-pointing spinous processes.

• Lumbar Vertebrae: Largest and strongest; short, thick spinous processes.

Thoracic Cage Components

• Sternum: Manubrium, body, xiphoid process.

• Ribs: 12 pairs; 1-7 are true ribs, 8-12 are false ribs (11-12 are floating ribs).

Fontanelles on a Fetal Skull

• Fontanelles: Soft spots on a fetal skull where bone formation is incomplete.

• Function: Allow for compression during birth and brain growth after birth.

Appendicular Skeleton

Overview and Components

The appendicular skeleton includes the limbs and girdles that attach them to the axial skeleton:

• Pectoral Girdle: Clavicle and scapula.

• Upper Limbs: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Pelvic Girdle: Hip bones (ilium, ischium, pubis).

• Lower Limbs: Femur, patella, tibia, fibula, tarsals, metatarsals, phalanges.

Landmarks of the Appendicular Skeleton

• Scapula: Spine, acromion, coracoid process, glenoid cavity.

• Humerus: Head, greater and lesser tubercles, deltoid tuberosity, olecranon fossa.

• Pelvis: Iliac crest, acetabulum, pubic symphysis, obturator foramen.

Pectoral and Pelvic Girdles

• Pectoral Girdle: Attaches upper limbs to the trunk; allows for a wide range of motion.

• Pelvic Girdle: Attaches lower limbs; supports body weight and protects pelvic organs.

Differences Between Male and Female Pelvis

Epiphyseal Plate in Juvenile Long Bone

• Epiphyseal Plate: Growth plate made of hyaline cartilage; site of longitudinal bone growth in children and adolescents.

Bone Fractures

• Types of Fractures: Simple (closed), compound (open), comminuted, greenstick, spiral, transverse, oblique, etc.

• Identification: Based on the pattern and location of the break.

Muscle Physiology

Key Terms and Definitions

• Muscle Twitch: A single, brief contraction and relaxation cycle in a muscle fiber.

• Latent Period: Time between stimulus application and the beginning of contraction.

• Contraction Phase: Period when muscle tension increases.

• Relaxation Phase: Period when muscle tension decreases and returns to baseline.

• Motor Unit: A motor neuron and all the muscle fibers it innervates.

• Threshold Stimulus: The minimum stimulus required to elicit a muscle contraction.

• Recruitment: Increasing the number of active motor units to increase muscle force.

• Summation: Addition of individual muscle twitches to produce a stronger contraction.

• Tetanus: Sustained muscle contraction resulting from rapid stimulation.

Phases of Muscle Twitch at the Cellular Level

• Latent Period: Action potential travels along the sarcolemma; calcium ions are released from the sarcoplasmic reticulum.

• Contraction: Calcium binds to troponin, allowing actin-myosin cross-bridge formation and muscle fiber shortening.

• Relaxation: Calcium is pumped back into the sarcoplasmic reticulum, cross-bridges detach, and muscle returns to resting length.

Role of Calcium in Muscle Contraction

• Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from actin's binding sites, enabling cross-bridge cycling and contraction.

Motor Neuron Control of Skeletal Muscle

• Motor neurons release acetylcholine at the neuromuscular junction, initiating an action potential in the muscle fiber, leading to contraction.

Muscle Twitch Graph and Phases

• A typical muscle twitch graph displays the latent period, contraction phase, and relaxation phase.

• Each phase can be measured in milliseconds.

Motor Unit Recruitment and Muscle Tension

• Increasing the number of recruited motor units increases the overall muscle tension (force) generated.

Wave Summation and Tetanus

• Wave Summation: Occurs when a second stimulus is applied before the muscle has completely relaxed, resulting in a stronger contraction.

• Unfused (Incomplete) Tetanus: Muscle fibers partially relax between stimuli; contractions are sustained but show some relaxation.

• Fused (Complete) Tetanus: No relaxation between stimuli; contractions are smooth and sustained.

Maximal Tetanic Tension

• The maximum force a muscle can generate when stimulated at a high frequency, resulting in complete tetanus.

Example: Muscle Twitch Phases

• Stimulus applied → Latent period (~2 ms) → Contraction phase (~10-100 ms) → Relaxation phase (~10-100 ms).

Additional info: The above content expands on the study guide points with academic context, definitions, and examples to ensure a comprehensive review for exam preparation.